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Reem M. Alomer, Shannon M. Conley, Muna I. Naash; Cone Outer Segment Protein Sorting Is Independent Of Outer Segment Structure. Invest. Ophthalmol. Vis. Sci. 2011;52(14):34.
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© ARVO (1962-2015); The Authors (2016-present)
Previously we described a simplified open cone outer segment (OS) structure in the retinal degeneration slow (RDS) and neural retina leucine zipper double knockout model (rds -/-/nrl -/-). These OSs are functional although they completely lack lamellae. Here we use this modelto further study cone OS morphogenesis and protein sorting.
Retinal sections were collected from adult nrl-/- and rds -/-/nrl -/- mice with WT and rds-/- as controls. Immunohistochemistry was performed to evaluate the expression and localization of OS proteins in cone OSs with and without lamellae (nrl-/- and rds-/-/nrl-/-, respectively). We used markers for OS plasma membrane (PM) (CNG A3), OS lamellae (S-opsin, cone transducin), inner segment (IS) (Na+/K+ ATPase), and connecting cilium (CC) (RP1). Transmission electron microscopy and immunogold labeling for PM vs. lamellae markers were used to further investigate OS structure and protein localization.
In the rds-/-/nrl-/- model we observed that IS, CC and OS membrane proteins were properly localized. Interestingly, However, in the rds-/-/nrl-/- double knockout retina OS CNGA3 (PM marker) immunoreactivity did not co-localize with S-opsin (lamellae) immunoreactivity compared to nrl-/- retina, indicating that the segregation and sorting of these proteins to different membrane domains are preserved in the absence of RDS and OS lamellae. Cone transducin immunoreactivity completely co-localized with S-opsin, consistent with our previous observations that rds-/-/nrl-/- OSs are functional.
Our data suggest that the photoreceptors of the rds-/-/nrl-/- continue to sort proteins into specific domains regardless of the lack of lamellae. These data suggest that cone OS protein sorting is independent of the formation of lamellae and is likely regulated earlier in the OS targeting pathway.
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